This invention relates to improved catalysts for polymerization of alpha-olefins, and more particularly, to catalysts for polymerization of alpha-olefins to products of improved morphology.
It is well known to polymerize alpha-olefins in the presence of catalysts generally comprising an organometallic promoter and a supported catalytic complex comprising an intimate association of reduced Group IVB and/or VB metal halides, divalent metal halides and one or more aluminum compounds. Such complexes typically are prepared by reaction of one or more higher valent Group IVB or VB metal compounds, support materials comprising at least one catalytically inert divalent metal compound, and organoaluminum compounds corresponding to the formula AlR.sub.n X.sub.3-n, wherein R is hydrocarbyl, X is halogen and 0&lt;n.ltoreq.3. Examples of such catalyst components are described in detail in U.S. Pat. No. 3,644,318 (Diedrich et al.), U.S. Pat. No. 3,901,863 (Berger et al.), U.S. Pat. No. 4,199,476 (Melquist et al.) and U.S. Pat. No. 4,233,182 (Hoff et al.), all of which are incorporated herein by reference.
The above-described catalysts typically exhibit sufficiently high activities in polymerization of alpha-olefins that useful products can be obtained without removal of catalyst residues. This, of course, leads to important advantages in terms of process efficiency. However, catalyst performance is not entirely satisfactory from the standpoint of polymer morphology.
While not wishing to be bound by theory, it has been speculated that the small particle size of the supported catalyst complex and/or the tendency of the complex to fragment during polymerization use, e.g., during pumping of catalyst component and/or due to the exothermic polymerization reaction itself, result in relatively high levels of small polymer particles and a relatively broad distribution of polymer particle sizes.
Whatever the cause, production of small polymer particles and polymer of broad particle size distribution is disadvantageous for several reasons. From the standpoint of polymerization process efficiency, high levels of small polymer particles can cause problems because the particles tend to accumulate in, and plug, process lines and filters. From the standpoint of handling and processing of polyolefins, small polymer particles and broad particle size distribution can be disadvantageous because polymer bulk density often is lower than desired and an extrusion and/or pelletization step often is required prior to processing.
In the past, various means for improving polymer morphology have been proposed. One approach has been to prepare supported catalyst complexes using support materials which, due to their size, shape and/or chemical composition, yield complexes that are improved in terms of morphology. See, for example, U.S. Pat. No. 3,787,384 (Stevens et al.)--supported catalyst complexes prepared from silica, alumina or silica-alumina support materials having particle size ranging from 10 to 500 microns; U.S. Pat. No. 3,953,414 (Galli et al.)--spherical or spheroidal supported catalyst complex prepared from hydrated magnesium chloride which has been melted and sprayed into a current of hot nitrogen or air through nozzles having orifices of appropriate diameter; U.S. Pat. No. 4,111,835 (Foschini)--supported catalyst complexes prepared from hydrated Mg chloride in the form of spheroidal particles of 10 to 70 microns; U.S. Pat. No. 4,104,199 (Hoff)--supported catalyst complexes prepared from hydrated Mg stannate support materials; and U.S. Pat. No. 4,233,182 (Hoff et al.)--supported catalyst complexes prepared from support materials which are divalent metal salts of phosphorus acid esters.
A second approach has been to pretreat supported catalyst complexes with minor amounts of alpha-olefins to form encapsulted particles of greater size and resistance to fragmentation. See, for example, U.S. Pat. No. 4,190,614 (Ito et al.).
A third method for improving supported catalyst complexes in terms of polymer morphology involves the use of modifying compounds. Thus, U.S. Pat. No. 4,039,472 (Hoff) discloses treatment of complexes of the type described in the aforesaid U.S. Pat. Nos. 3,644,318 and 3,901,863 with anhydrous HCl to improve polymer morphology. Anhydrous HCl also can be used for purposes of temporary and reversible deactivation of supported catalytic complexes as taught in U.S. Pat. No. 4,130,699 (Hoff et al.).
Among the foregoing methods, the first is somewhat limited in terms of the number of materials that will yield the desired effect as a result of chemical composition and by the cost and complexity of obtaining support material particles of specific shapes and/or sizes. Similarly, alpha-olefin pretreatment is disadvantageous because it can add cost to the overall polymerization process. In addition, encapsulated catalyst complex particles resulting from pretreatment often are more difficult to convey and feed to a reactor than untreated particles.
The use of modifying compounds to improve supported catalyst complexes in terms of polymer morphology is potentially a simple and inexpensive method assuming the existence of effective and easy-to-use modifiers that do not adversely affect catalyst performance, e.g., activity, polymer rheology, to a substantial degree. Anhydrous HCl meets these criteria for the most part though its use is complicated somewhat because it is used as a gas, and accordingly, difficulties may be encountered in metering the precise amounts necessary to attain desirable improvements in morphology while avoiding undesirable agglomeration of particles or other undesirable effects.
From the foregoing, it can be appreciated that there remains a need for improvements in the above-described supported catalyst complexes in terms of polymer morphology. It is an object of this invention to provide such improvements. A further object is to provide supported catalyst components that are improved in terms of polymer morphology with only minor decreases, or in some cases, increases, in catalytic activity. A further object of the invention is to provide an improved alpha-olefin polymerization catalyst component and catalyst based thereon, as well as a method for production thereof and for use in polymerization of alpha-olefins. Other objects of the invention will be apparent to persons skilled in the art from the following description and the appended claims.
We have now found that the objects of this invention can be attained by modification of the above-described supported catalyst complexes with appropriate amounts of oxygenated compounds of phosphorus. Advantageously, the modification procedure is simple and does not add substantial cost to the overall polymerization process. Further, as a result of the modification, catalyst complexes are improved in terms of polymer morphology without substantial adverse effects on other properties. In particular, particle size is increased and particle size distribution narrows such that process efficiency is improved and polymer processing and handling are facilitated. Further, in some cases, these desirable results are accompanied by increases in catalyst activity.
In the past, various phosphorus compounds have been proposed for use in polymerization of olefins, albeit for purposes unrelated to morphology improvement, and such proposals may be of interest with respect to the present invention. These are discussed hereinbelow.
U.S. Pat. No. 3,186,977 (Coover, Jr. et al.) discloses polymerization of propylene and higher olefins, mixtures thereof and mixtures with ethylene in the presence of catalysts comprising a trihydrocarbylaluminum, a titanium or vanadium halide and a phosphorus compound corresponding to the formula P(O)Y.sub.3 or PY.sub.3 wherein Y is alkylamino or alkoxy of 1 to 8 carbons. According to the patentee, use of such a catalyst, particularly in propylene polymerization, gives products of increased inherent viscosity and molecular weight and substantially higher crystallinity.
U.S. Pat. No. 3,216,987 (Price) discloses polymerization of C.sub.2-20 alpha-olefins in the presence of titanium trichloride, alkylaluminum dihalide or sesquihalide and alkyl- or aralkylphosphonates. The phosphonate component and the alkylaluminum component are combined prior to addition of the titanium trichloride. Price discloses that polymerization in the presence of such catalysts gives polymer of improved crystallinity.
U.S. Pat. No. 3,278,643 (Achon) discloses that addition of an organophosphate, organothiophosphate, organophosphonate, organophosphine or organophosphine oxide to a vanadium oxytrichloride-alkylaluminum dihalide gives increased activity in polymerization of mixtures of ethylene with higher olefins to substantially non-crystalline polymers.
U.S. Pat. No. 3,377,326 (Loveless et al.) discloses addition of phosphorus trihalides in combination with oxidants to a primary olefin polymerization catalyst system made up of a vanadium salt and organometallic component to increase polymerization activity, particularly in copolymerization of ethylene and propylene.
U.S. Pat. No. 3,639,375 (Staiger et al.) discloses olefin polymerization catalysts comprising a titanium(III) halide-aluminum halide complex, an amine, a phosphite of the formula O.dbd.PR.sub.3 or O.dbd.(PR.sub.2).sub.2 .dbd.O wherein each R is independently hydrogen, hydrocarbyl or hydrocarbylamino, an organoaluminum compound and, optionally, an organozinc compound. The catalyst is useful primarily in polymerization of propylene, with the amine and phosphite components serving to promote activity and/or stereospecificity.
U.S. Pat. No. 3,644,320 (Sugiura et al.) discloses addition of trithiosphosphates or trithiophosphites to titanium trihalide-organoaluminum compound catalysts to improve stereospecificity without decreasing activity in polymerization of C.sub.3 or higher alpha-olefins.
U.S. Pat. No. 4,186,107 (Wagner) discloses supported catalytic complexes prepared by contacting a specially prepared magnesium halide with electron donors, including phosphines, and titanium halides. According to the patentee, an essential step in preparation of such complexes is treatment of magnesium halide particles with donor either during or after precipitation of such particles. Column 9 lines 1-12. The result is treated with an aromatic acid ester and then titanium halide, after which an optional electron donor treatment may be conducted. Column 11 lines 32-45.
U.S. Pat. No. 4,222,895 (Allan et al.) discloses heating of titanium trichloride and phosphorus oxytrichloride in the presence of methylene chloride to improve catalyst efficiency and stereospecificity.
An abstract of European No. 5639 (Stauffer Chemical) discloses the use of phosphorus halide, preferably PCl.sub.3, to stabilize vanadium tetrachloride.
An abstract of Japanese No. 52-100,595 (Mitsui Toatsu) discloses catalysts prepared, in part, by grinding titanium trichloride with certain phosphorus compounds.
Unlike the proposals discussed hereinabove, the improved catalyst complexes of the present invention are prepared by contacting preformed supported complexes containing reduced titanium halides with certain phosphorus compounds. Further, the results of such contacting--improving the complex in terms of polymer morphology--are neither disclosed nor suggested in such proposals.